Hi,
Welcome! Regarding Canon cameras, only those before 300D are good for IR. Exposure is not that long(between 1 to 10 secs, depending on weather). Personally tried on 300D with Edmund Long Pass Filter, Cokin P007 and Hoya R72. Have seen EOS 10D in action, the exposure is about the same as 300D. Can auto focus too!
As for Powershot A series, I've tried A80 & A95 with R72 filter, exposure is about 1 sec, but some time, camera hunts alot.
Shall not comment on G3 as I didn't have. For 20D, its not so good for IR actually, exposure is extremely long, easily 30secs! And also, only works with R72. With Cokin P007 and Edmund Long Pass Filter, you will not be able to Custom White balance, all you get is a red image. I won't recommend 20D.
Ok, for 350D, I believe will be like 20D, as Canon's hot mirror seems to be getting stronger and stronger! So exposure should be very long.
Long exposure caused motion blurs, some time can be appealing but not most of the time.
Hope this help
Cheers
Max 2.8