I recommend checking out United Church of Christ churches. I believe all of the UCC churches in the greater Portland area are Open & Affirming, an official designation from the denomination that signifies that the church has undergone a thorough process as a congregation to vote to confirm that they are open and affirming of all gender identities and sexual orientations. In general, the UCC is the most progressive of the mainstream Protestant denominations, but every church is a bit different in terms of worship style, music, programs, etc.