I had arranged to barter with a guy for spray foam the attic. And he hurt his back. I was going to have him spray 2" and blow-in on top. I am in MN. I have many 6" recessed cans, round insulated attic ducts on the bottom cord of the trusses. MgO board ceiling and no poly vapor barrier. Any out of the ordinary ideas of options instead of spray foam?

If the MgO is detailed to be air tight you could use a spray-on vapor retarder.

Vapor-retardent latex primer such as Benjamin-Moore's SUPER SPEC. LATEX VAPOR BARRIER runs ~0.5perms in a single coat (similar to kraft facers), about half-that in 2 coats. In a vented attic configuration that should be enough, given that 2" of closed cell polyurethane runs about 0.6 perms.

http://www.benjaminmoore.com/DownloadBinary?fileName=20110330+260+TDS+US+OKF.pdf&nodeId=BEA+Repository%2F16126&propertyId=BEA+Repository%2F16126%2Fdata_sheet_file_en_US

It can go on either under the ceiling paint, or on the insulation side of the MgO, or both.

Air tightness is key though- a full shot of closed cell foam is pretty good, but it's not the only way to get there. The roof deck will be the condensing surface, but the dilution factor of outdoor air in a vented attic would be more than enough to keep up with vapor permeation, but not necessarily with massive air leaks. Sealing over & around all of those light cans & power penetrations may take a full day of detailing with 1part foam.

You might want to read this carefully before applying even vapor-retardent paint to the interior side of the ceiling:

http://www.buildingscience.com/docu...nload/file

It's highly likely that the MgO and truss chords will stay drier if you used only standard latex on the interior and just left it at that, and let the attic ventilation deal with protecting the roof deck (which it surely will.)