Originally Posted by omatase
The wife and I would like to put together an arbor for a grapevine we have in our backyard that's something along these lines....
...She looked at cedar but couldn't find anywhere that would sell non-rough cedar...
Just because your wife couldn't find smooth cedar doesn't necessarily mean that its not available.
Its possible that she didn't know where to look. I'm guessing that she looked at the Big Box stores first?
You might have better luck finding your material somewhere that caters more to professionals.
Your post didn't indicate where you are so I can't be of much help there.
Try Googling "hardwoods" or "lumber" in your area and see what pops up. Call around. The suppliers you contact may nor have what your looking for but may be able to refer you to a supplier that does.
The arbor in the link is nice looking but IMO would be much less attractive built with pressure treated material.
Not knowing what tools you have at your disposal.....
You could buy rough sawn lumber and run it through a planer to smooth it but you'll lose some thickness.
As far as finishing techniques and products go I'll have to abstain from commenting.
Other folks here are much better qualified in that area than I am.
I hope I've helped a little at least.