When using the notation patches in GPO4, the sustain pedal (CC# 64) does not activate legato, but rather holds the note as a sustain pedal normally does. After poking around the forum, I get the impression that CC# 68 may activate legato in the notation patches, but after playing around with it for a while, it doesn't seem to do the same thing.
CC# 68 certainly does affect the sound, but in a different way from 64. I have a slider on my MIDI keyboard set to send CC# 68 on channel 1 with a notation patch set to channel 1 and the equivalent standard patch on channel 2. This way, I can rapidly switch back and forth between the two and perform the same phrases over for each. CC# 68 does seem to take some of the attack off of the notes on the notation patches, but in a very exaggerated way compared to 64 on the standard patch. I have tried setting the CC value to different levels just in case the effect was variable over a continuous spectrum, but there are no CC values that produce the same sound as CC # 64 in the standard patches.