First off Seward/Seaward isnt my branch of genealogy, but I would love to try to help you if I can at all. I have been working away on mine, and others genealogy for over 13 years now, my most prominent area of research is Newfoundland.
It is very common for individuals within the same family to have varying spellings for their surname, - a lot of the time it was due to enumerators etc spelling things as they sounded, so you end up with the same person spelt 3, 4 or more different ways in documents.
It is actually Trois Rivieres, Quebec - just so you find it in records easier. I have been through there a couple times during travels.
I do see a Patrick, E. Seaward in the Newfoundland Navy,
1139X Seaward, Patrick E. Boston, MA
Patrick can be found in the 1935 Gooseberry Bay, Census which contains MANY other Sewards...highly likely close family.
SEWARD Patrick E Jr Head M M 42
SEWARD Winnifred Wife F M 32
SEWARD Edward Son M S 14
SEWARD Cecil Son M S 12
SEWARD Eileen Daughter F S 8
SEWARD Patrick Son M S 5
In the 1921 Census, although I didnt find YOUR patrick, I did find this as a possibility, This family has a father living with them, a widower by the name of Patrick. Could possibly be the father of your Patrick, and his namesake as was very common.
I also find a Patrick Seward in 1920 on a ship list for the Rosalind, departing St, Johns Nfld to Halifax, Nova Scotia. This Patrick has $200.00 in his possession, born c.1893, states he intends to work in the ship yard and is from Quebec.
I will keep looking to see what else I can find for you, as soon as I get some more free time. Feel free to email me directly if you wish,firstname.lastname@example.org