Without photos or a more detailed explanation, it is difficult to understand what you want to do but in general, the tops of any brassicas - if cut from their stems - will not root or grow into new plants. What you are asking is rather different from the OP's question re: the offshoots or suckers from the base. And even those won't grow on their own without a root system.......

I have only been able to find mixed pks at Canadian Tire

Those are beautiful plants - I assume they taste just as good as the other kales? I had a terrible time getting my kale (Red Russian) started this year, had to resow 4 or 5 times. I now have about 8 plants. But those are growing so well that its plenty. The current favorite recipe is to take a buncha leaves, cut out the tough part of the stems, then roll the leaves up and shred them as finely as possible with a very sharp knife. Then mix up a vinaigrette, add thinly sliced onions, dried tomatoes, some slivered almonds, and toss it all together, and let it marinate for at least two hours before eating.

May be the Cabbage Looper or the Imported Cabbage Worm. The Imported Cabbage Worm is the larva of a small white butterfly and is a pale green color when munching on the leaves of the cabbage family. The Cabbage Looper is a pale green with yellow stripes larva of a small mottled brown moth. Both prefer the undersides of leaves and will be there all the time until they fall off to pupate. The easiest means of control, with just one or two per leaf, is squishing, but if many more are present dusts of Bacillus thuringiensis - Kurstaki can help with control.