Long shot

Rainy Lake in the Washington North Cascades just west of Winthrop is a great accessible trail. It's asphalt and level and about a mile into the lake.

Forrest Park in downtown Portland! It has great trails (thankfully only a mile from my home) and has a slightly bumpy, but paved, trail that extends the entire length of the park.

Many of the short hiking trails off of the Cascade Lakes Highway that heads into the mountains from Bend, Oregon, are reasonably stroller-friendly. Walker lake is a particularly beautiful short hike you can take. Also, there are paved trails in the Land-of-Fire area south of Bend. I believe the Lava-Cast Forest trail is partly paved, as are some of the trails in Lake Paulina N.M.

I'm assuming that you mean a "child stroller". You may try looking into "accessible" trails in the Northwest. I want to say that I've seen books on the topic but I'm not entirely sure. You definitely won't be able to get too long of a trail, but you may be able to find a couple that are maybe a mile long or so. Off the top of my head, it seems like some of the trails in Silver Falls State Park are paved. I believe the trail is paved all the way to the South Falls. State parks in general probably hold the greatest hope for finding paved trails or boardwalks that are accessible to wheelchairs, or strollers.