I just phoned them and it looks like the 115 will work. I asked if a
900/1800 phone would work and the nice lady said that as long as it would
accept a SIM card and was unlocked then it would work. I patiently await
delivery of my phone from the UK. I'll post updates under this thread.

My guess is no - Rogers is GSM 850/1900, yes?

I've really been wanting one of the ultrabasic Motorolas - the C115,
117, or 118.
I can't, however, seem to find any of these models in anything but GSM
900/1800.

I did call Motorola USA to see about it, but they were (predictably)
unhelpful.  The woman who was unlucky enough to field my call couldn't
find anything about the phone in her database - apparently they only
have info on the phones that are widely available in their country.

So, you're out of luck, as far as I can tell.