Definitely get a postal scale. I got mine from Staples. Your basic limits for parcels to the USA are up to 249 grams, up to 499 grams, and up to 999 grams. You can check online at canadapost.ca to find out what it will cost to ship each parcel, you put in the weight, dimensions, and destination, and it tells you what the cost will be. The cheapest method of shipping to USA is "Small Packet Airmail". However, this option does not include insurance or tracking. You can also send by "Small Tracked Parcel" which is the same thing, but costs about $8 more and includes delivery confirmation and insurance. That is, insurance against loss: fragile items are not covered by insurance.
For inexpensive items, I charge an extra $2 per parcel for insurance, and then cover them myself. For expensive items, anything over $40 or so (that is my comfort zone, that is how much I am willing to risk being out of pocket), then I ship those the more expensive way.
Shipping overseas gets trickier, it is more expensive, and you have to be careful shipping ponies to some countries.
I always label my customs forms with 'collectible figurine' rather than 'toy'. I don't put 'my little pony' on the customs forms, to avoid theft.