Jean,
I expect you'll have to purchase the registration - i don't think there is a listing of them outside of the MB Archives. However, a search of the 1901 census turns up a Clara Grantham and a James Brennan in the same area, and of about the right ages for a marriage 8 years later. This is the only Clara Grantham in Westbourne at the time.
1 10 3 Grantham George M Head M Aug 22 1844 56, b. ON r, English, Methodist, farmer
1 11 3 Grantham Eliza F Wife M Sep 30 1846 54,b. ON r, Irish, Methodist
1 12 3 Grantham Oliver G. M Son S Apr 9 1874 26, b. MB r
1 13 3 Grantham John W. M Son S Jun 17 1878 22, b. MB r
1 14 3 Grantham Wm. C. M Son S Nov 10 1883 17, b. MB r
1 15 3 Grantham Prudence F Daughter S Oct 10 1880 20, b. MB r
1 16 3 Grantham Emily A. F Daughter S Dec 19 1885 15, b. MB r
1 17 3 Grantham Clara A. F Daughter S Feb 8 1887 13, b. MB r
1901 Census of Canada
Subdistrict: Westbourne, MACDONALD, MANITOBA
District Number: 8
Subdistrict Number: n-1
Archives Microfilm: T-6433
5 2 36 Brennan William M Head M May 5 1857 44, b. I r
5 3 35 Brennan Ellen F Wife M Aug 1 1858 42, b. W.S. r, emig 1870
5 4 36 Brennan William M Son S Mar 8 1879 22, b. ON r
5 5 36 Brennan James M Son S Jul 6 1885 15, b. MB r
5 6 36 Brennan Margret F Daughter S Jun 23 1887 13, b. MB r
5 7 36 Brennan Lonzy M Son S Nov 22 1889 11, b. MB r
5 8 36 Brennan M. Ida F Daughter S Apr 29 1882 8, b. MB r
5 9 36 Brennan Harry M Son S Oct 25 1895 5, b. MB r
5 10 36 Brennan Ibena F Daughter S Nov 21 1897 3, b. MB r
5 11 36 Brennan A. John M Son S Dec 3 1899 1, b. MB r
1901 Census of Canada
Subdistrict: Cypress (North/Nord), MACDONALD, MANITOBA
District Number: 8
Subdistrict Number: b-3
Archives Microfilm: T-6433
1906 census:
4 272 Grantham Geo. Head M M 63, b. ON r
5 272 Grantham Elizabeth Wife F M 61, b. ON r
6 272 Grantham Clara Daughter F S 18,b. MB
District: MB Portage la Prairie District (#6)
Subdistrict: 13 (Townships 13, 14, 22, 27, 30 in ranges 10, 11 west, townships 15, 20, 32 in ranges 11, 14 and the Town of Gladstone) Page 38
Details: Schedule 1 Microfilm T-18355
Residing at 22-14-11-W1
Some food for thought anyway.
Bette
PS - I could use a lookup for a birth record in Ontario, but I'll email you about that offline. Thanks