Having lived in Seattle I wouldn't think it would do well. The hills would be a big factor. Even on a road bike, getting around beyond downtown generally involves a climb that is difficult. Maybe you can go from the industrial area south, through downtown, and then up through Belltown and into the Lake Union area. You could even ride up Eastlake into the U-district, but that's about it without encountering a good climb. You'd be better off walking to Capitol Hill, First Hill, Queen Anne as you'd never make it up. Maybe Rainier Valley is doable. Basically it is a north-south corridor that is relatively flat, but it gets hilly going anywhere else, and you can still encounter hills anywhere, even east-west in the narrow downtown area.

The other factor there is that I don't find it particularly friendly to cycling, in spite of it being considered cycle-friendly. Maybe certain areas are, but I hated being on a bike in Downtown, whereas I ride all through Manhattan without a second thought.