Change one thing. lon-dfw-sea instead of lon-lax-sea. AA doesn't have a direct LAX-SEA flight, so you will avoid a segment charge. Otherwise, it is fine.

old:
1. yvr-nyc
2. lax-sjc
3. sjc-sea
4. sea-dfw
5. dfw-mia
6. mia-dfw
7. dfw-yvr

new:
1. yvr-nyc
2. dfw-sea
3. sea-dfw
4. dfw-mia
5. mia-dfw
6. dfw-yvr

I don't know the rules as far as returning to your origin city, as those are different for the US and Canada when compared to everywhere else. Talk to the RTW desk and see if you can go into YVR more than once. That would save you a bus ride.