Insubstantial Copying

The Copyright Act C-42 states: "3. (1) For the purposes of this Act, 'copyright', in relation to a work, means
the sole right to produce or reproduce the work or any substantial part thereof."

Therefore, insubstantial use of copyrighted material does not violate copyright. 

How much is "insubstantial"?

The Copyright Board of Canada defines insubstantial use as:

"1 to 2 pages of a work, not constituting more than 2.5 percent of the entire work.”

 Although they are referring specifically to print, it applies equally to other media. Note that short excerpts of video or audio must be obtained from legal copies without breaking a technological protection measure (digital lock).

More than Insubstantial Amounts

If you need to copy more than an insubstantial ammount, then use Fair Dealing to estimate what is permissible.