Re: need advice on getting photos printed large/canvas

Michael Reichmann has a video tutorial with Jeff Schewe ("From Camera
to Print") that has an entire chapter devoted to resolution questions
like you are asking.
Here are some points made in that video:

Upressing to 200% usually is not a problem.
With a good capture (tripod, good lens, etc.) 400% is possible.
If you upres in CS3 then use "Bicubic Smoother."
However, the real key in upressing files is to properly sharpen them.
The best tool for this is Photokit Sharpener (I can vouch for this
one).

Viewing distance determines the needed resolution.  At viewing
distances over 24" 180ppi is sufficient.  The "normal" viewing
distance is twice the diameter of the pic.

For the photo you mentioned I would probably upres to 200%, preferably
in Camera Raw.  Then I would sharpen to taste.