I have a few midi sequences that will reset all sounds( besides drums) to piano. I use a Roland SC-88 pro sound canvas with powertracks. Sometimes when I start the sequence, then I stop and press the 'Midi devices' tab, then press ok, sounds will be correct for bass, strings.. This is rare, but do I need a program change of some kind?
Yes
Each MIDI channel needs to know what intrument it is supposed to play.
Powertracks can do this via Patch Change dialogue, or for true MIDI use the Event List to insert a Program Change.
Yep, exactly what Rharv said - your MIDI sequence likely has a Program Change at the beginning which is changing the instruments back to Piano.
Right click on the track and choose Program, then set the instrument you want, OR go to Window > New > Event List, and remove the Program Change.
Probably you'll have to erase the system exclusive information (Sysex), normally found in the first or second track. Powertracks provides an editor for that.