You might want to post on Belarus Ancestry board.
I have no Ancestry subscription so the first place I look in www.ellisislandrecords.org
I did not look on each arrival manifest but even if your ancestor went directly to Canada possible that other family member could come to America first and then go up North.
Demczuk, Pawel Teleshinci, Russia 18 1895 1913
Demczuk, Pawel Kriwluki, Russia 22 1891 1913
Demczuk, Pawel Dworety, Russia 25 1886 1911
Demczuk, Pawel Pautjuk, Russia 19 1891 1910
Demczuk, Petor Mikulin, Russia 20 1893 1913
Demczuk, Petr Jushkovicz, Russia 24 1890 1914
Demczuk, Petro Siroka, Russia 33 1879 1912
Demczuk, Pjotr Smoljary, Russia 38 1874 1912
Another thing, I did not look if the locations are now in Belarus.
Do you have a place of birth for your grandfather?http://archives.gov.by/eng/