The emphasis of the Weaver commentary in Nature is that 1) less than 10% of the oil sands are economically viable to be extracted 2) even if 100% of the oil sands could be extracted using new technologies the total volume of released carbon dioxide would be negligible compared to the real concern which is coal.

When you say "this one project" I think it betrays a misunderstanding of the scale, scope and complexity of oil sands extraction. The oil sands are "one project" much in the same way as "middle-eastern oil" being one project. Oil sands are complex chemically and geologically with surface extraction projects and deep subsurface extraction projects. Each project itself should be looked at since some are very carbon intensive and some are comparable to conventional oil in carbon intensity.

As for Dr. Weaver, he is a modeller (one of the originals) and using his model if all the hydrocarbons in the oil sands were mined and consumed, the carbon dioxide released would raise global temperatures by about 0.36 C. When only commercially viable oil sands are considered, the temperature increase is only 0.03 C. Coal and natural gas supplies would increase global temperatures by 15 C and 3 C respectively.

If you want cogent discussions on oil sands (both positive and negative) I would direct you to http://andrewleach.ca/ Dr. Leach has a very good set of reference links and does a decent job discussing the technicals on the subject.