Location is in Canada / Ottawa
I did a web search, but I can't figure out what species it is.
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This is very likely an araneid (or Orb-weaver spider) in the family Araneidae.
Without further evidence/details, it's hard to narrow down to a species.
One possibility is Larinioides sclopetarius (the bridge spider or gray cross spider).
Source: Ed Nieuwenhuys
Prosoma grey to grey-brown. Opisthosoma grey to grey-brown, dorsally with pronounced, white margined pattern. [Source: University of Bern]
Range: holoarctic including Ottawa, Canada
What it's NOT
Although visually similar, this is not Nuctenea umbratica (walnut orb-weaver)
The specimen is also unlikely Larinioides ixobolus, which generally has a black outline (vs white) on their backs And is constrained to Europe/Asia:
Possibly incorrect, but it looks like some kind of orb weaver - from the shape of the abdomen and the posture, it's very similar to a lot of orb weavers and potentially is in the Araneus genus.
I don't think it's this species, but you can perhaps see the similarities; http://www.spiders.us/species/araneus-diadematus/#more_pictures
It could also be an immature, hard to know :/