RE:MERGERYes the difference will narrow, as this is called arbitrage. People will go long Medreleaf and short ACB to get the difference.
You can buy Medreleaf right until it is delisted and when it delisted your shares will be converted for each Medreleaf share into 3.575 Aurora shares, and lets be honest this is the best time to get in.
I have put up some things why Aurora is a better buy then Canopy, and can be seen on the ACB board.