I think you're really overanalyzing the mushroom risotto. Crème brûlée isn't a dish associated with Canada. Neither is risotto. Or chocolate cake. Or hamburgers. But they have to serve something, so they put Canadian twists on a variety of dishes that might be eaten in Canada but aren't necessarily 'Canadian cuisine'. I'm not going to criticize them for that. What would you suggest they serve with their filet instead of risotto? Should they be limited to poutine (fries with cheese curds and gravy)
I don't think the truffle butter has an off-putting flavor. I really like it. I guess since I care less about the 'flavors' of the beef (as long as it has the flavor of a filet), I'm fine with a nice sauce accompanying it. And apparently the other signature restaurants feel the same way (California Grill has a smoky teriyaki barbecue sauce, Jiko has a South African cabernet reduction, Flying Fish's strip steak is served with a creamy sauce foyot, etc).
No, I wouldn't say mushrooms are a popular food in the US. They're something that picky eaters especially dislike. And given the wide number of picky eaters that frequent WDW, it impresses me that a dish with heavy mushroom flavor is so popular. On the other hand, my info search about Canadian cuisine indicates that mushrooms are very popular in Canada, which makes sense as they're strongly associated with the Pacific Northwest.
I'm not criticizing Le Cellier for serving risotto. More of just wondering out loud, whether it is a very common and popular dish in Canada. You'd find it odd if Le Cellier started serving pizza, sushi, and jambalaya.
Crete brûlée, is not surprising. Just as baguettes are not surprising in Hanoi. If you have been to Montreal, the dining is much like being in Paris (where Creme brûlée is even more prevalent than apple pie in the US)
And yes, I also dislike the Teriyaki filet at California Grill, and wouldn't order it. As I said, it's pretty rare I order a "steak" in a restaurant. If I do order a red meat dish, it's more likely to have a very light sauce, such as a gastrique, maybe a simple red wine reduction.
But soaking a piece of meat in a heavy butter or thick sweet BBQ sauce, is not a way to enhance complimentary flavors.
I had an amazing meal for my anniversary a couple weeks ago. Pricey -- about $200 per person. The best dish was a tiny slice of chicken breast served with carrots. No sauce at all. But the chicken, free range, farm fresh, was the most tender, most moist, most flavorful I ever had in my life. The carrots tasted nothing like any other carrot I've ever eaten.