It's private property. You will be trespassing. They will probably bring you to a room at the base and have you sign a form stating that you will never step foot on their property again, in return for them not pressing charges.
Maybe it won't be that bad.... but I've asked similar questions in the past and not received a warm reception. Definitely call ahead and I think you will find that they tell you in very clear language that it is not allowed. If I remember correctly; even if you buy a downhill bike pass, there are very clear signs saying that you are not allowed on the service road (with a few exceptions where the road is the trail.)
If you are on their property and you haven't agreed to a liability waiver, it's a huge issue for them. What if you are coming down and you hurt yourself on a trail and then you sue them for not having a safe trail? The liability waiver on every ticket is in place to protect them from that risk.
At Cypress Mountain, if you want to access Black Mountain, Bowen Lookout, or other trails in the provincial park, you have to cross through a very short section of active ski resort (they don't own the land but they have an operating certificate to run a resort in that area of the park.) As a result, you must go to the service desk and get a free pass that basically just has a waiver on it saying that you won't sue if you get hurt during the time you cross the short section of active ski area.
Technically, I believe WB does not own the property, just the tenure to run a ski hill, same as Cypress I'd assume. It would be prohibitively expensive for them to own it.
As Crown land, my impression is that they can't stop you from being there, but as they are liable for anything that happens because of their tenure and it's development (ie: you wipe out on one of their roads), so you are not going to get any doors opened for you by asking, especially if you are proposing to participate in an activity that circumvents their established (and documented for insurance purposes) safety mechanisms, such as biking outside of the established trail network without having signed a waiver.
As for trespassing, I don't think they can do anything legal; normal practice for those breaking the rules of their pass agreement (for example, riding on closed areas like roads) is to blacklist someone from the facility for "X" amount of seasons. Sans pass, you might get escorted off the tenure and documented. Don't think there's much they can do to you if this isn't leverage on you.
It is frustrating that bikes continue to be banned from most of Garibaldi Park but Whistler is allowed to run a for-profit bike trail in the alpine at the top of the mountain and heli-skiing companies are allowed to access the park in the winter. It's hard to reconcile all those facts.
I have to respectfully disagree here. Both have their purposes: the bike park/ski hill drives visits and creates jobs for the resort and the people that live here, and the park is mandated to protect the eco-system within it's borders, while making it accessible to users in a non-destructive way (hence the no bikes in sensitive areas). Both are world-class attractions. They mostly make good neighbours. If there was to be an infrastructure built in the alpine for lift accessed biking, it might as well be where the ski hill and resort is, and keep other more pristine, sensitive and less accessible areas undeveloped for the self propelled. Gotta have something for everyone. Heli-skiing is a different animal, don't think I want to get into that in this thread.
If Whistler was going to allow uphill bike travel within the area of their resort, they would have a similar program set up (kind of like the program they have for one-ride-up skiiers in the winter.) They don't have that program - you can't offer to sign a waiver.
For the record, WB does allow and has endorsed uphill to downhill rides though their MTB park via the local cycling association, WORCA. Obviously these community Loonie races/rides take place when the trails are otherwise closed, and participants need to be WORCA members (as such, are insured through the assoc. ) to ride. Thus far this has not been offered to individuals, as it would conflict with their current user/business plan, and would be a nightmare to manage to boot. Since there is a huge selection of pedal access trails managed in the valley by WORCA (supported in large part by donations from WB), it would seem unnecessary for them to allow uphill bike travel within their area of the resort.
A couple other pertinent points:
WORCA actually is developing a self-propelled access alpine riding trail over the top of Sproatt Mountain to meet the demand for an alpine MTB trail, outside of the provincial park (as it should be). I imagine this trail will be finished using all the lessons learned from many years of building resilient MTB park trails in our local climate and conditions, to ensure longevity and protect those local areas.
Also, everything I've mentioned above is just based on my experience and observation coupled with the many conversations I've had with WB employees regarding these exact topics, not any special access or insight.
It's worth noting that all of these "rules" are flouted nearly everyday by skiers/boarders/bikers/hikers, either ignorant or willfully ignoring the agreements that are made to ensure the long-term good will necessary for continued access. I personally often hear of friends/acquaintances organizing night rides down Singing Pass trail or over the BT Meadows, or co-workers scamming passes for ski days, someone pedaling up Blackcomb for a beer at the Horstman hut, dirt bikes on ski runs, or local news articles about illegal camping/squatting in residential neighbourhoods or on the ski hill(issue is trash/human waste disposal). It really is no wonder that it's been an issue for WB.
Seems like it's often "cool" to "stick it to the man" by ignoring the user agreements when it's anonymous or financially advantageous, but the hue and cry that goes up when those agreements are enforced and punitive measures are contemplated...
I guess the long and short of it is, there are tons of places where you can ride up to the alpine, why is it a big deal if WB discourages it because they are liable for any accident? IMHO, I'd rather pedal up Blowdown or Sproatt anyway. Less ATV dust.