It depends where Global really ends up,
That really is the million dollar question.
but if it stays on 6, we are stuck requiring VHF-lo (Global), VHF-hi (CTV) and UHF (the rest).
Don't forget CBOFT. It will likely end up reverting to channel 9, so it will also need VHF-HI.
Since OMNI is moving down we will probably require from a 2-51 solution.
That is a given. No one will be allowed to use channels 52-69 post transition.
Do you think the best low price options for local reception would be something like a CM3018 or CM3020?
Those would likely be overkill for central Ottawa, as there likely isn't any hope of receiving American stations (except maybe most parts of Orleans, but they should really have their own thread). If Global stays on 6, I think a CM3014 or CM3016 would be good enough as a single antenna solution, though a rotor would likely be necessary.
A two antenna solution (pairing a vhf antenna like an antennacraft CS600 or Antennas Direct V15, with a CM4221) may be a better bet. VHF pointed to camp fortune, UHF on rotor or midway between manotick and CF. However this may complicate some.
I agree a two antenna solution would be much a better option, though, as you say, it might be a bit too complicated (or bulky) for some. The choice of UHF antenna really depends on your exact location. For many a reflectorless antenna would be best, but a CM4221 is a good start.