First part. Yes, you can have provider 1 on MX 1 (primary) and provider 2 on MX 2 (spare).
Second part. As long as VRRP packets make it across the switches & wireless bridges the MXs will work in HA mode. My concern would be reliability of the wireless link and if you drop VRRP here and there you could end up with both MXs thinking they're primary (dual master issue).
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