/Library/Frameworks/Cairo.framework/Resources/dev/lib/libCairo.dylib: mach-o, but wrong architecture)
You have a set of native Gtk+ libraries from somewhere else. They're not Apple's; you can try
pkgutil --file-info /Library/Frameworks/Cairo.framework/Resources/dev/lib/libCairo.dylib
to see if there's an Installer receipt for it. You'll probably need to remove all the related frameworks as well, and may then need to force rebuild the MacPorts libraries in case they managed to tangle themselves up in the unexpected framework(s).