However, that being said, the only Sarah Tweed that I can find in the census who would be about the right age is:
11117Tweed WilliamHeadMW45, b. England, emig 1886 12117Tweed William H.SonMS13, b. MB 13117Tweed Sarah E.DaughterFS11, b. MB 14117Tweed SamuelSonMS9, b. MB 15117Tweed Edna A.DaughterFS7,b. MB 16117Tweed WilfridSonMS4, b. MB District:MB Marquette District (#5) Subdistrict:03 (Townships 13, 14, 15 in ranges 21, 22 west) Page 15Details:Schedule 1 Microfilm T-18355
But there are two good candidates for William Reid, both 15 and both in Marquette, one who is b. England, emig 1903 and living along with an Irwin family but who seems the most likely because he's living closest. (Subdistrict:05 (Townships 13, 14, 15 in ranges 25, 26 west) cPage 33.) He "sounds like" a British Home Child but that's just a guess on my part.
The other William Reid is the son of Alexander and Revina Reid but is living a little further away at Subdistrict:07 (Townships 16, 17, 18 in ranges 27, 28, 29 west) Page 26.
Unfortunately, it looks like you'll have to spend you money this time to find out I suppose.
Assuming the above is the right Tweed family, however, then the mother was Christina Wood (she's listed on the following births) LAST NAME: TWEED FIRST NAME: EDNA ANNIE DATE OF BIRTH: 03/18/1899 PLACE OF BIRTH: R.M. OF DALY SEX: F REGISTRATION NUMBER: 1899,005223
LAST NAME: TWEED FIRST NAME: WILLIAM HENRY DATE OF BIRTH: 07/23/1893 PLACE OF BIRTH: R.M. OF DALY SEX: M REGISTRATION NUMBER: 1893,001957
LAST NAME: TWEED FIRST NAME: SARAH EUPHEMIA DATE OF BIRTH: 12/29/1894 PLACE OF BIRTH: R.M. OF DALY SEX: F REGISTRATION NUMBER: 1895,002345
LAST NAME: TWEED FIRST NAME: SAMUEL DATE OF BIRTH: 03/13/1897 PLACE OF BIRTH: R.M. OF DALY SEX: M REGISTRATION NUMBER: 1897,005511
Marriage for Wm & Christina GROOM'S LAST NAME: TWEED GROOM'S GIVEN NAMES: WILLIAM BRIDE'S LAST NAME: WOOD BRIDE'S GIVEN NAMES: CHRISTINA DATE OF MARRIAGE: 04/25/1893 PLACE OF MARRIAGE: DALY REGISTRATION NUMBER: 1893,001688
Possible death for William Tweed (father) LAST NAME: TWEED GIVEN NAMES: WILLIAM DATE OF DEATH: 11/04/1935 AGE: 74 UNITS OF AGE: YEARSSEX: M PLACE OF DEATH: BRANDON REGISTRATION NUMBER: 1935,044004
1901 census: 10 25 105Tweed WilliamM HeadMApr16186238, b. Eng, emig 1886, Church of England, farmer 10 26 105Tweed ChristinaF WifeMMay24187525, b. Scotland, emig 1886, Presbyterian 10 27 105Tweed William H.M SonSJul2318937, b. MB 10 28 105Tweed Sarah E.F DaughterSDec2918946, b. MB 10 29 105Tweed SamuelM SonSMar2018974, b. MB 10 30 105Tweed Edna A.F DaughterSMar1818992, b. MB 1901 Census of Canada Subdistrict:Blanchard, MARQUETTE, MANITOBA District Number:9 Subdistrict Number:d-4 Archives Microfilm:T-6433
Samuel Tweed signed up for WWI as a single man, listing his residence as Oak River, Manitoba and his father William as next of kin.
William Henry Tweed also signed up listing his b.p. as Morris MB and his current address in 1918 as Oak River. Also single, also listed father as next of kin.
I hope some of this is ringing a bell and tells you whether or not this might be the right Tweed family.