Just to add on - the Peak Forest and the Macclesfield are good starting points.
Our good friends at Manchester Canoe Club in the Dale can be of help for slightly more adventurous places.
Brookbank Canoes of Stockport have the use of part of the Roman Lakes.
Yes, you are supposed to have a BWB non-powered licence to use the canals which turn out to be quite expensive (and they have been known to check - just like fishing licences) - so why not take out BCU membership which is much cheaper and covers canals and gives you insurance and lots more!
www.bcu.org.uk.
Remember paddle safely.