I see what you're saying but I feel like this situation (hypothetical GSW/Thunder-Raps matchup) is slightly different. I think it could potentially bring in more money and a bigger fan base for the future.
On top of the whole 'underdog vs champs' narrative that would inevitably follow (which isn't particularly unique) they'd be able to frame it as a Canada vs U.S. comp. Not explicitly pinning nations against one another but just emphasizing the fact that a Canadian team has never made it this far in the NBA and how big of a deal this is for the Raptors, their fans, for Canada making it's mark in professional basketball etc. etc. This opens up the opportunity to get a lot more Canadians interested in the NBA, which has already been happening this year... people that didn't know anything about the league or the sport itself and had zero interest in it before have hopped on the bandwagon even since just yesterday (not complaining, I think it's great). There's so much hype around the Raptors within Canada now that it's impossible not to notice the team and what's going on around them - on the news, people flooding downtown for playoff games, 'we the north' slogan. A lot of Canadians are just thirsty as hell to start winning and to have a good sports team that's worth cheering for representing the country.
The NBA is predominately American now but appealing to and involving Canadian crowds more would be smart, here's my theory:
Professional sports tend to bring out nationalism in people which can seriously increase the size and commitment of fan bases. Nationalism just makes shit a lot more intense.
Think about the World Cup. How many people watch it and how much money is rolling in. It's not just because everyone loves soccer (most people never watch soccer outside of the WC). It's also because it encourages people to express their national pride in competition with other countries and 'prove the superiority of their own' or whichever they feel represents them. As weird as that may sound since these usually aren't conscious and calculated thoughts for most FIFA fans irl, the people doing marketing/advertising for FIFA and sports leagues in general are well aware of this. Might be slightly problematic ethically imo but marketing-wise it's definitely a good strategy for bringing in bigger crowds and money because, while only a small percentage of the population are die hard soccer fans, the vast majority of people are patriotic.
Anyways this ties into why I can't see Americans being put off of the finals. In our sub and r/nba whenever there's a raptors game you can always count on there being some Canadian-American bs brought into the discussion e.g. Wade disrespected our anthem, or just two salty fans going back and forth reverting to ripping on each others countries because it's the most immediately apparent difference between us and hence easiest to call out whilst salty af. The NBA has no shortage of marketing skills. They would run with this because it's an interesting/new narrative and hence there would still be hype lol.