Dual sim as in the ability to have two sims? That's popular in India and the middle-east, so Motorolas yes probably. But that's not what's required for Fi.

IIRC Fi's requirement has to do with the ability of moving phonecalls smoothly between wifi and cellular. This capability used to be limited to a dozen or so phones. I don't know what the state of this is nowadays.

Edit: https://www.androidcentral.com/these-phones-work-project-fi -- I don't know which ones are good on that list, to be honest. I really liked the 6P, although it was a bit too large for my taste. I miss phones like the S3 :/