Does letter of invitation serves the purpose as "purpose of visit" or she has to write a separate letter for "purpose of visit"?from what the experts says here the length of visit as a visitor should keep in 2-3weeks only plus make a detailed day by day itinerary from the 1st day til the last day of visit with estimated cost of trip. For the ties, make sure that she has more ties in her country than there in canada which is u as husband.. Her ties in her country should be stronger than staying in her husband.. If she has properties under her name, family that dependent to her like they need her to takecare of them personally you can include them to her letter of explanation with evidences.
Applying online or paper doesn't matter.
Goodluck ~
Thanks katt for helping me in this..