The log shows:
:info:build ld: warning: ignoring file /Library/Frameworks//libpng.framework/libpng, missing required architecture x86_64 in file
:info:build ld: warning: ignoring file /Library/Frameworks//libtiff.framework/libtiff, missing required architecture x86_64 in file
:info:build ld: warning: ignoring file /Library/Frameworks//libjasper.framework/libjasper, missing required architecture x86_64 in file
Please delete /Library/Frameworks/libpng.framework, /Library/Frameworks/libtiff.framework and /Library/Frameworks/libjasper.framework; they are not part of MacPorts and are interfering with MacPorts. Then "sudo port clean opencv" and try again.