Will you be doing a lot of flying between Halifax and Washington?
Maybe 3 times a year. I'm more concerned with using award tickets where I don't have to transit through the US. And I wasn't sure if it was easier with Air Canada miles or United miles, or if it made a difference at all. The other thing is, so far I've earned all my miles and points through credit card usage and if I continue using the starwood card in Canada, starpoints transfer to United at a rate of 2:1, I didn't see what Air Canada transfers at.
If thank you points flights have to originate in the U.S. why can't you have every flight originate in the U.S.?
DC - YHZ (outbound)
stay as long as you want
YHZ - DC (inbound)
I don't know

I guess the only drawback is not knowing when I want to come back to DC and I'm not sure if there are any rules for completing travel within a certain number of days but if that works, @:-)THAT'S BRILLIANT@:-) and thank you so much for suggesting it.