It all depends on which part of the Fraser River you are fishing and what species you are targeting.
If we are talking about locations downstream from Mission, tidal influence is a tremendous factor as the difference in water height between high and low is significant. Generally I find that the fishing is excellent just after the tide peaks for about two hours, depending on how fast it is dropping. If it drops very fast, then the magic period is shorter. If the drop is slow, then the magic period is longer. This rule has worked well for bull trout, cutthroat trout, coarse fish, coho. It works either by bait fishing on the bottom or spincasting.
For chum and pink salmon, I've found that incoming tide is best. From low to high, it's not unusual to spot schools of fish finning as they swim up the river with the tide.
Steelhead is not specifically targeted in this section of the river because there is just too much water, and the amount of fish is no where near the number of salmon. Of course it is not impossible to encounter one by the same methods, but you would be spending much more time just to connect with one.
For the section above Mission, although there isn't really a visible difference in water height, tidal influence exists as high as the Harrison River (again, depending on the tidal difference of the day). Barfishermen plan their outings so they coincide with the incoming tide. Make sure you add the correct number of hours to the Vancouver tide chart.
For cutties, availability of food is a bigger factor. Coastal cutthroat trout are constantly on the move until they come across the food they eat, ie. eggs, small fish, junveile salmon, etc.