TiPb contacted Rogers to get some clarification about that $20 "add to existing data plan" option that was listed on Apple.com today as part of the Canadian iPhone pre-order launch, and Rogers was kind enough to respond:

We've confirmed that we have two iPad data plans available for our customers. Both the 250 MB for $15 and 5 GB for $35 include free unlimited access to all Rogers WiFi Hot Spots.

At this time, we do not have a sharing plan to announce. The reference to a sharing plan on the Apple website was an error and is being removed.

Please visit RedBoard for more information on iPad data plans

On the RedBoard, Rogers further notes that their Fido subsidiary will not be supporting the iPad at launch.