pinniped

Pick your 3 cities first. Then figure out what the best Marriott options are. I'd look at everything: cash rates, hotel categories for awards, and which of the cities you'd really want to spend a full week in.

With 700k Marriott (and nothing else), my target approach would be to redeem two Marriott Travel Packages and do the third city as a paid stay. You *could* do all three as regular hotel award stays, but I personally value the TPs so much that I'd be willing to accept paying for some nights where it made the most sense.

Once I was looking at 3 cities, it would probably become evident where to redeem. 1 of my cities would maybe have really good rates, or no great Marriott, or it just works out that I'm only there 4-5 nights and it makes sense to just look for a good hotel deal even if it's not Marriott.

Also note that 240,000 miles in a different alliance could come in handy if you're having trouble finding Aeroplan award availability one direction or the other. There's a thread on the Marriott board about how fast they post miles to various airlines: it's usually quite fast.