IMO Michigan would have more opportunity than Cali at this point. The House/Senate here just had a bill on the table right before the session came to an end and they almost crammed it through. There is bi-partisan support so it will get done very soon. Even though dispensaries aren't officially legal, there is a shit-ton of them already.
Cali is saturated with weed shops, where as Michigan is an emerging market with a ton of opportunity. I can't argue the weather angle though if sunshine and warm weather is a consideration.