1) my 2014 Chevy sonic has wheel bolt pattern of 5 X 115 while the elantra has 5 X 114 . Can I use elantra rims on sonic or the slight difference is a concern.

2) Can you use winter tires in the rear wheels and all season at front and is this legal in most areas of Canada or States

sorry, Sonic is 5X 105 so the elantra rim will not be compatible.

The slight difference would still be a difference, so the answer would be no.

I've never heard of laws about this, but you should check with your local authorities. I'm not sure why anyone would want to do this on a front wheel drive vehicle. In winter, it would make more sense to put the winter tires on the front wheels. In summer, running winter tires on hot roads will wear them out faster.

Definitely.

Besides bolt pattern, you also need to be aware on centerline offsets.