A Canadian football field fits at Lamport - just get rid of the parking lot at the south side of the stadium. Extend each stand the remaining 35 yards or so down the new field - that in itself would expand capacity by a few thousand, and perhaps provide an opportunity for new CFL changerooms to be built. Then add private boxes and a second deck on top of each existing stand, and you've got a 20,000-seat stadium.
https://www.flickr.com/photos/809020...posted-public/
The expanded stadium is feasible; it's just a question of political will, the right funding formula, and whether the residents of Liberty Village will put up with this as you say.