With your limited time and lack of experience, I would suggest that a trip up the Macclesfield Canal would be your best, and most enjoyable, option. There are just 12 locks at Bosley and you should easily reach Marple and back. At Marple you can then decide whether to continue up the Upper Peak Forest to Buxworth (no locks, but several lift/swing bridges).
If you want to see Marple Aqueduct, I suggest you walk down the 16 locks of the Marple flight.
To give you a rough idea of journey time, allow about 12 hours from Heritage to Marple.
The Shropshire Union is a varied and attractive canal (arguably not as attractive as the Macc & Caldon) but there is no way you could get there and back on your holiday.
Cheers
Phil
(in Congleton)