Most people when they think of OTA, they think of visiting weird old Aunt Mona who had a big honking antenna on a long mast, and got one channel in snowy wonder, back in the 1950's.   They don't think of a setup like mine that gets 18 channels with 16 of those being 5 out of 5 and 8 of those being in HD.

I would expect that among those with OTA a much higher percentage have ATSC capabilities, in major centres like Toronto.  In the back of the beyond, I doubt that many have it and it's probably not a good thing for them anyway, since digital is all or nothing. 

I would expect that if the transmitter is going to stay at the same power on the same frequency it would just be adding the encoder to the process before the transmitter. If it's changing to less power it's probably just replacing a board or two in the transmitter, most expensive part would be the engineering to decide how much power is needed for the same coverage.  With the limited coverage TVO has, this would be a good opportunity to greatly increase their range for little money.    I would assume they will remain largely SD.  In schools and other educational facilities, there is no real need to be HD, I expect the number of circa 1990 style VCR's being used in schools, and big old tube style TV's is still quite high, and it will be 2029 before that is all replaced.