Tokyo to Shin-Osaka is less than 3 hours using a Japan Rail Pass. The trip from NRT airport into Tokyo is about an hour on the Narita Express, so around 4 hours from NRT to Shin-Osaka. Then a few minutes on the subway or cab to wherever you need to go in Osaka. There are several Osaka stations.

If you arrive in Tokyo at Haneda (HND) instead of NRT, the trip to a bullet train station is about 20-30 minutes instead of an hour from NRT.

For only $94.00 difference, I'd definitely take Air Canada instead of Air China. The reduced travel time and avoiding PEK would be worth that to me. YMMV.

If your plan turns out to be flying into Tokyo - either NRT or HND - then train to Osaka, then some other travel and finally train back to Tokyo and then out to NRT, all within 7 days, then the Japan Rail Pass definitely makes monetary sense. Just remember that you must purchase the Rail Pass BEFORE you arrive in Japan. You can usually get it a large travel agencies or on-line. They will sell you an exchange order that will have to be turned in at the JR station before it can be used on trains. Make sure your round-trip travel NRT-Tokyo-Osaka-Tokyo-NRT all falls within 7 days.