the videos that I recorded on my Canon DSLR are nowhere to be found
Usually, even deleted files are still on the disk until they are over written by some other file. Try running file recovery software such as Recuva or Puran. Be sure to read the software user guides before starting.
However, I once got caught out looking for files on a card when the device was actually saving to it's built in storage. I am not aware of any canon DSLR with built in storage though.