As a branch off topic,When ever I fly the 747, The FMC usually climbs at around 265 in vnav, is this allowed for heavies?

Yes. Read the full FAR regarding the speed restriction;

Sec. 91.117 — Aircraft speed.a. Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).b. Unless otherwise authorized or required by ATC, no person may operate an aircraft at or below 2,500 feet above the surface within 4 nautical miles of the primary airport of a Class C or Class D airspace area at an indicated airspeed of more than 200 knots (230 mph.). This paragraph does not apply to any operations within a Class B airspace area. Such operations shall comply with paragraph (a) of this section.c. No person may operate an aircraft in the airspace underlying a Class B airspace area designated for an airport or in a VFR corridor designated through such a Class B airspace area, at an indicated airspeed of more than 200 knots (230 mph).d. If the minimum safe airspeed for any particular operation is greater than the maximum speed prescribed in this section, the aircraft may be operated at that minimum speed.

Most people don't get past paragraph a., which is where the confusion on the topic sets in.

I believe in Canada, they can waive the restriction, but ATC still can't request higher than the speed limit.

Yes, in Canada, on departure, once complying with Noise, if your cruise level is above 10,000ft you can accelerate to normal climb speed below 10,000ft. The 250/10k restriction does not apply.In the US, normally, 747s and heavy 777s are exempted as well as their typical minimum clean speed is better than 250 knts.* Orest