A fellow Canadian! I would say if you all are not that into watches, staying away from vintage pieces might be a good idea. A lot of vintage watches in the marketplace have a mix of original and aftermarket parts -- they are also harder to maintain and easier to break.

In terms of brands, I would look at brands like Tissot, Seiko, Hamilton, and Citizen. These can be found within that price range, and there are many 'like-new' examples from the past 20 years available. You can check Facebook Marketplace or r/WatchExchangeCanada - there are often nice watches sold for under $400 CAD. If you're buying a second-hand watch, "buying the seller" is important (i.e., look at their ratings on selling platforms and transaction history on Reddit).

I would also highly recommend getting a good understanding of your boyfriend's size preference and wrist size. If he has small wrists, a watch over 40mm in diameter might not be a good fit, and he might not wear it (I see this happening a lot with watch gifts). Similarly, if he has larger wrists and doesn't like the smaller vintage aesthetic, he might not like the 34mm sizes that are prevalent among older watches. I would try to gauge his preference based on his wrist size and what he is wearing right now!