I can only give you my experience. I booked that offer the day it came out, not knowing it was a Canadian offer until later. I called Disney to change something on my reservation, and asked specifically about it and if there would be problems ect. The first person I spoke to said absolutely not, you've already booked it, no problem, they won't ask for a Canadian ID ect. However, they couldn't change anything on my reservation, so they had to get me to guest services. I spoke to a lady there, and again asked specifically about all of it, and she gave me her name ect., and said there wouldn't be a problem, but she had to figure out how to change what I needed changed and she'd call me back. A couple days later, she called back, and change what I needed changed and she again said it would be no problem, it was Disney's fault for allowing the US addresses ect., and the fact that nowhere on the online booking does it say anything about needing to be a Canadian. She gave me her name and told me there'd be no problems when checking in.
Honestly, if they come out with
free dining for US (which I'm sure they will,) and I remember and have time, I'll probably cancel my Canadian reservation and book again, just to feel better, but having said that we just returned from Disney and could have booked the bounceback, but I never got around to it, so I must not be that concerned.
ETA: By the way, the only way I learned it was a Canadian offer, was from the disboards. If I wasn't on here ect., I would have never known.