I don't think it's related to a holiday campaign for a few reasons (for reference, I work in advertising so this is actually something I know about!)
Simons does an annual holiday campaign with very specific art direction and photography - they're pushing their cozy knits and a lot of the design assets feature this minimal box with bow graphic, and the chunky type treatment used on all of their main headlines. I can almost guarantee that if the billboards were part of a larger holiday campaign they would have to feature the same creative for consistency. All of these holiday campaign assets have a very specific look and feel that I'm just not seeing in the digital billboards here.
There is no CTA pushing people to the website since there is no local store, and none of the copy reflects the rest of their holiday messaging. Nor does the imagery align with the rest of their holiday assets.
Ad space is incredibly expensive, and I don't understand why Simons would purchase billboard space as part of a holiday campaign and not use their holiday creative (which, again, is very expensive to produce)
The billboards at the well look like generic brand awareness assets - if they wanted people to shop online there would be specific messaging pointing the viewer to visit the website, shop online etc. I can't fathom a reason they would develop and produce these assets, purchase space for them, and run them in this very specific location where ad impression numbers are probably not yet known due to the complex not being open and operational. Why not at Yonge and Dundas where there are thousands of holiday shoppers out every day?
I think there's more to this, but again, I really don't believe this is part of a holiday campaign based on the inconsistencies with the creative alone.