then canal all the way into Manchester city centre
The canal is closed between Portland Basin and the bit where it goes under the A6140 (just south of J23, M60).
There is a diversion but it’s not well signed at all. And no, bikes cannot get through, it is properly closed. Fine from there on though, the bit past the velodrome etc into the city centre is all fine.
The road routes in from Huddersfield are horrible; either busy A-roads or steep / narrow (and often busy) valley roads like through Slaithwaite. If I absoilutely had to ride it I’d come in via Meltham and the Isle of Skye road (A635) into Greenfield then turn left by the Royal George pub and use the B-road (B1675, Well-Hole Road which becomes Huddersfield Road) into Stalybridge, Dukinfield and Audenshaw and jump onto the canal there for the last bit.