They're not cognates.

'kanskje' = 'kan+skje' = 'may+happen', while 'kans' is related to 'chance', which would be 'sjanse' in Norwegian.

It's related to misschien (which comes from older forms of "(het) mag (ge)schieden"), but instead of "mogen" = må (which in Norwegian means "must") it took kunnen = kunne.

Notice how similar these are: "misschien" (Dutch), "måske" (Danish), "kanskje" (Norwegian) and "kanske" (Swedish) all meaning "maybe" or even the similarly constructed "mayhaps".