If I were you I would avoid choosing Sympatico. They are overpriced, they block ports and they force you to rent a modem for $10/month from them forever. Furthermore their customer service is made of brainless drones who "only support IE browsers" and have only been trained to give support to "senior" customers who are using their windows pc for the first time, but the agents are completely useless for anything technical. Rogers is no better. They cost even more and cap their service to something ridiculous like 60 gigs/month or whatever, and if you go over the limit they simply suspend the service as a "punishment" for a couple of weeks, but they still charge you.
What I would advise you is to take a look at
http://canadianisp.com/ for a comparison of ISP's in your area.
A lot of people on can.internet.highspeed recommend teksavvy (check it out at
http://www.teksavvy.com/ ), they serve Ontario and Quebec. As the name suggests, it is a cheap (but quite good) ISP oriented towards technically minded people. If it wasn't for the downtime hassles I would certainly switch to them. Currently I pay $29.95/month for unlimited bandwidth and I have bought my own ADSL modem/router. Compare that to what Bell is charging.
Regarding the use of a DSL modem on the Amiga, all of the DSL connections in Bell territory are set by default to pppoe, so that should be enough to get your Amiga compatible with just about all modems (correct me if I am wrong). On the other hand you could buy a router with a built-in adsl modem, that way you won't have any problems using it with the Amiga as long as you have an ethernet card. That's what I did.