The best video format for iMovie goes to apple intermediate codec, the .AIC file format.
This is the guide about how to convert canon Vixia video to AIC for editing in iMovie.
First download canon Vixia video converter for mac, the software supports to convert canon Vixia videos to AIC format, also various output video formats are supported, but AIC is the best for editing in iMovie.

Import canon Vixia videos, set output profile as AIC.

Convert canon Vixia videos to AIC format for editing in iMovie
Now you can fully enjoy the mojo of iMovie with your new video.
