Me, personally, it's not a big deal. But in several ways Canadian identity is based on comparing ourselves with the United States, as if it were the only relevant comparator. I see this in policy and people's national identification. So, I do think a good number of Canadians dislike being mistaken for Americans because it doesn't align with their identity. Separate from that - and the context of this post is travel - there's a popular idea amongst Canadian travellers - especially the hostel-going type - that the world perceives Canadians better than Americans. So, many will display Canada flags when they travel to preemptively fend off the idea that they're American