Zeus, the canal is strange, and quite unpredictable, especially at this time of year when the striped bass migration is not in full swing.
That being said, I'll take a stab at answering your question, based on what I've seen personally and notes I've made in my log book. When the tide is dropping, the current flows west into Buzzard's Bay. When the tide is rising, the current flows east into Cape Cod Bay.
For fishing the Scusset end of the canal this time of year, I've had the best luck on the rising tide, as the canal empties out into the Cape Cod Bay. My theory is that resident bass will hang just outside the main current,in the cooler water of the Cape Cod Bay, and wait for bait to be flushed out of the canal to them. The same could be said for the other end of the canal on the oposite tide, but to a lesser degree, as the Buzzard Bay waters are quite warm right now, and in my opinion, most decent fish would prefer to hang in the cooler water at the other end, even if it's only a few degrees cooler.
Even with that theory in place, it's been sketchy lately. Not much seems to be around but schoolies. Another thing I've noticed is the distinct absence of bluefish. Usually this time of year, I'm having to battle the blues to get to the bass. Yet, I haven't caught a bluefish since we had a batch of big ones come through in late June. I even broke tradition, and fished during the daylight with metal to see if I could find any, and came up empty.
Once the migration south begins in earnest, we'll start to see some really nice fish come through the canal. In the mean time, don't be afraid to get skunked.