Degrassi

Goosebumps
Mullet kid serving pastries "Calling all Creeps" later appeared in:
 * s2e01 (When Doves Cry part 1) Paige points out "that's a mullet"
 * s2e02 (When Doves Cry part 2) in the mall waiting in line with friend before JT notices Paige wearing sunglasses ~5 minutes in
 * s2e11 (Don't Believe the Hype) ~7 minutes in at cultural festival after Paige's Ukrainian costume is discussed, seen behind Spike as he eats cake
 * s2e18 (Dressed in Black) ~9 minutes in, after a view of the front of the school seen with friend crossing in front of Tobey right before he puts condoms in JT's locker and then Spinner discovers them. Friend seen behind Emma and JT
 * s2e19 (Fight for Your Right) near the end in the computer lab seen in blue jacket behind goth girl
 * s2e22 (Tears Are Not Enough) ~halfway as Paige dances with Spinner and JT with Liberty (Manny?), is holding the limbo pole as Emma and Sean limbo underneath
 * s3e1 (Father Figure, part 1 ) at the start, after Spinner's teacher points out he is repeating 9th grade English and Paige assures him "noone was laughing hun" he is seen following his friend directly behind Paige right before the camera cuts away.
 * s3e3 (~5 min in) right after JT says "so I like her, big deal" seen behind him as he and Tobey look up to see Manny's new appearance, and as it zooms in on JT he is smiling
 * s4e4 (Mercy Street) pushing bullied kid against locker

Continuum
The abusive father the focus of season 2 is a major character

Lost Girl
Tracker Cameron is Dyson, also in "Touch of Pink"

Westphall
According to http://web.archive.org/web/20131001000255/http://home.vicnet.net.au/~kwgow/crossovers.html it is one of at least 15 non-US shows, along with Doctor Who.