You may find a 220V supply is already available in Canada. Although normal outlets are 110V, most premises will have a second 110V feed for use on high power appliances already and between them you will get 220V.
You can't take the feed from two sockets and combine them. As the sockets will be on the same AC phase there will be zero volts between live and live and also zero volts between neutral and neutral so it will not produce extra voltage. Warning: if you try that you could also bridge sockets fed from different fuses which would present a serious safety hazard.
In general, yes you can reverse a transformer so 'step down' becomes 'step up' and I would guess in most instances the wire rating would be similar on both sides so it should work. I would allow say 20% over rating just in case though. A 3000W one used with a 2200W load should be safe.
If you use the roti maker on 110V it might work but the heat it produces would be much less. If it has a thermostat to regulate the heat it may just take longer to reach operating temperature then work fine but it if also has any motors in it, they may not develop enough power to 'push' hard enough, especially if you are also going from 50Hz AC to 60Hz AC.
Brian.