Is invitation Letter needed for visiting Canada for 2 days?

[exuberantbliss]

hello!

Can anyone help me finding an answer to a simple query, which seemed to put me in a merry-go-round ride?I'm planning to stop by Toronto for only 2 days  on my way to New York from Dubai? I plan to apply for visitors visa. Is it mandatory to have an invitation letter for a visitors visa even if the stay is only for 2 days? My son( who's 8 yrs old) and my mom would be accompanying me. We don't have any friends or relatives there who can send us an invitation letter. Will the hotel where we're staying provide us with an invitation letter?..but again I don't think so they'll do that..
The purpose of visit is just tourism .. ie my son is going head over heals to see Niagara falls..
so, please any one ..I would really appreciate , if you could tell me whether it's necessary to have an invitation letter for the visit visa even if our stay is not going to extend beyond 2 days...