After boating for a number of years, I've been through almost all the tight spots. The following assumes minimum 40' boat with 8 knot speed, and proper research and situational awareness.
Port Townsend Canal: There is plenty of room for single file traffic meeting, current can be challenging for slower boats. In my towing days, we used to routinely tow 180' x 50' barges with wood chips with an 80' tug drawing 12'. Every now and then, we'd bring log rafts through which could be 150' wide and 450' long. It worked fine if the tug stayed in the deep water channel. For those interested, check out 33 CFR 162.235a in the Coast Pilot 7 which specifies whistle signals prior to entering the canal, and a 5 mph speed limit. While the regulations are very old, there are still a few complaints from time-to-time from beach owners concerned with beach erosion caused by boats creating large wakes.
Swinomish Slough: Pretty straight forward as long as you have done your research for adequate draft, and air draft for sailboats. In my towing days, we occasionally would tow a 220' x 45' x 10' draft barge through here with a 10' draft tug. Even today, there are log rafts towed through here where they require most of the channel, but there is usually enough room to stay out of the way. Watch for minimum speed requirements, they may patrol for them in the summer months.
False Narrows: I like going through here because it eliminates the slack water congestion at Dodd Narrows and offers a much larger transit window. I use 7' of tide for my 4' of draft, a little current will help keep the kelp down.
Boat Passage: This spot requires some careful research and local knowledge. I wouldn't go through here the first time without taking your tender out on a preceding slack water and checking it out. There's about 30' of width available at high water slack, which is 45 minutes before Active Pass slack. If there are large tidal exchanges, the slack water doesn't last long. Also, actual slack may vary from book time up to 20 minutes depending on weather conditions and atmospheric pressure.
The Gut: High water spot only. We used to take our 40' boat through here frequently between Telegraph Harbor, and fishing at Porlier Pass. There should be water level gauges indicating water depths in the canal at the entrance markers at each end, but these are sometimes unreadable due to growth.
A few other spots: Canoe Pass, just north of Pass I in Deception Pass, is about 40' wide, slack water only. Pender Canal requires close observance of tidal height and air draft, remember those soundings are in meters.