Which company provides the most cost effective residential broadband plan in Toronto ?

I am considering to buy a 99$ Apple TV adaptor. i.e large chunks of data to be downloaded.

I think I'll be in need of at least 50 MBit/sec downloading speed plus 100 GB /month bandwith.

Also, Has anyone had any experience with ISP, TekSavy ?

Can't really offer any advice on the ISP choice but 50mbps is possibly more than you need (unless you have a number of people in the house who will all be simultaneously streaming HD). Even then, with HD it's still keyframes followed by small delta frames streamed at variable bit rates. In other words, you'd still do well to exceed 50mbps.

Also bear in mind there are no services yet that offer audio (other than stereo) on their streams. Audio uses a huge chunk of bandwidth but this is something we don't have to worry about just yet.

I've run some tests here, I've had multiple HD streams running on one PC and single streams running simultaneously on the other computers. No problems, no stuttering or buffering and we "only" have 20mbps.

Broadcast HD here is 8GB per hour, which works out to about 18Mbps. However, I'd presume that HD over the Internet is likely to be H.264 rather than MPEG-2, so that would be using far less bandwidth. I don't have any problem playing 1080P from Youtube with a 5Mbps connection but some of the online trailers at other sites are too much for it.

Unless you are fully Mac in house, I’d consider many of the other Media units newer technology, higher spec, more options, AppleTV is old proprietary and only handles up to 720p, although it can ‘output’ at 1080p and it can’t actually process a video at this resolution.
I’d look in to other media centers, WDTV, popcorn hour, LG etc

I second the recommendation for Popcorn Hour - I love mine. you can stream across the network or stick a hard disk inside it and then drop files on to it. 1080p and mkv support.