One thing that you may have overlooked with wxtide is that it can also give
you 'time of current' as well as 'time of tide' information. I haven't checked
to see if one exists for the canal, but if you check the list of locations that
you can set, some of them have a (C) next to them, which means that there is
current information available. If you select a location with a (C), it will
show you a slightly different type of chart which shows the current flow over
time.
Hope this helps,
-- Tom