Victoria
1 (or 2) on the viaduct just to the W. Relatively straightforward, requires slewing the P6 line southward, should be then space for 6 cars.
Use - Northern services via Salford Cr, whichever you like.
Deansgate
A new single line, south of the existing on viaduct from the CLC. Very expensive, but you asked
Use - stopping trains ex Warrington, allowing an increased frequency, assuming the option of a tram-train to Irlam is not taken.
Cheaper alternatives: a single-platform terminus at Cornbrook or Pomona; the former would be challenging, the latter probably has space but would require a pedestrian bridge over the canal.
ISTR NR are looking at the Victoria one, but are concentrating on the rebuild of Oxford Road.