It would be a good idea to contact your local police and have them contact the nearest military base for explosive ordnance disposal assistance.
That would appear to be a 76mm Armoured Car projectile. Unfired. Made in the United Kingdom. Possibly High Explosive Squash Head. Shell body was manufactured in Nov 1978 by Royal Ordnance Birtley.
In Canada they were fired from Cougar Direct Fire Support Vehicles. These used the same turret as the British Scorpion. The round could have originated from a variety of places:
-Early Canadian buy of ammo from the UK.
-British stock from Suffield, I'm pretty sure they had Scorpions there.
-It's a repainted drill or display round, most of which were UK manufacture.
Any other painted markings on it anywhere?