Celebrity itineraries may not include Glacier Bay. IIRC, only Princess and Holland America offer them. Holland America also tends caters to a near-geriatric crowd so there's less "youthful" entertainment than Princess which tends to be middle age (FWIW).

Transfers between Seward/Whittier and Anchorage are also horribly expensive (somewhere in the region of $80 pp).

Holland America and Princess quite frequently offer reduced rates (as much as taxes and fees only) for the 3rd and 4th passengers occupying a cabin. Holland America is also reducing sailings out of Vancouver (had as many as 4 ships this season - 2 weekly R/Ts out of Vancouver and 2 plying Vancouver-Seward on opposite rotations), but is putting a big ship (Nieuw Amsterdam) next season so may be harder to get good fares.

If you might be susceptible to sea sickness, cruises from Seattle nearly always go around the ocean side of Vancouver Island instead of travelling up the sheltered inside passage which is more interesting (too bad the passage is usually at night - was at a location where I could see the ships loitering around on the inbound to Vancouver and steaming fast or slow depending on the tide at Campbell River).