We use the Pacific Hwy truck crossing all the time with our 29' long TT. Going into Canada there is fine. Going into the US through the Nexus lane is really tight though and forces you to swing wide into the adjacent bus & commercial truck lane. The regular lanes are okay and we see lots of large/long FWs & TTs all the time. Exiting the US booths has some concrete barriers designed to slow people down which makes for some fun maneuvering. We have never used the Peace Arch crossing but have heard that since it got rebuilt a few years ago, it's really easy for RVs. We've also heard that the Sumas crossing is also easy now that they recently rebuilt that too. I'd foget about the Pac Hwy crossing.
Surely you can't be going into Vancouver with a FW behind you? Unless you're heading up to Whistler/Pemberton area or the Sunshine Coast. If heading towards Hwy #1 east of the Port Mann bridge, you can head up hwy 99 and take the new #17 South Fraser Perimeter Road over to the #1 hwy as on the map below. Or take Hwy 11 from the Sumas crossing right up to Hwy #1 and from there go west towards Vancouver or east up the Fraser Valley. The Guide Meridian in Bellingham will take you right up to the border, but I would avoid it in and near Bellingham as it gets very busy and is slooow. One easy way over to Sumas is via H road parallel to the border starting at the Pac Hwy crossing.
Sorry for the fuzzy map, it's all I could find. Hwy 11 is north/south direction east of #15 on this map.