They are both great guns .
I personaly like having one of each which solves the dilemma.
If you can only have one there are some things that tip the scales in either direction.
If accuracy is paramount a longer barrel 617 will probably outperform a 63 but expect much more muzzle weight especially with a 6" barrel.
If you intend to pick up a Model 686 in the future get the 617.
Likewise, If your intention is to get a J frame 38 or 357 and want a partner gun the 63 is the wiser choice.
If you will only be terminating tin cans and prefer a smaller frame over a larger one the 63 is the better bet, Especially if you have small hands.
When teaching beginners, girls almost unanimously prefer the smaller lighter J frame .22. and guys like the larger K frame.
I didnt know Canada had restricted barrel lengths.
If 4" is a "Bad" gun and "6" is ok?....What about a 4.5" or 5" barrel?