When it comes to getting MP Transformers (or any Japanese Transformers release), importing from Japan is definitely the way to go. Even if you factor in the shipping cost, you still come out ahead of any Canadian or US website.
The best place to get Transformers that are already released would be Mandarake:
https://order.mandarake.co.jp/order/
They sell pre-owned items. But that does not mean they are opened and used. They have an excellent assortment of Transformers that are brand new and sealed in addition to stuff that have been opened and used. They are very clear on the condition of the item in the description. Mandarake has very high standards so even if the item is used, you would be hard pressed to find any difference between a new and used item.
The prices are also very fair. I sometimes pass on certain pre-orders and end up regretting it. When I end up buying it from Mandarake, it is often the MSRP price or perhaps even lower depending on the demand for that item.
If I have to pre-order, here are my go-to websites:
https://www.amiami.com/
https://hlj.com/
Both offer very good prices and shipping rates. However, they declare the full value of the item so if you buy something crazy expensive like MP Beast Wars Megatron, expect to pay very heavy duties on it when it passes through Canadian customs.
My personal go-to is Nippon Yasan:
https://www.nippon-yasan.com/
People often say the customer service for NY is not as good as Amiami and HLJ. I agree but NY offers a huge advantage since they automatically undervalue all items they ship. That Beast Wars Megatron is 28000 yen? Well, they will say the package is only worth 30 buck so you won't be charged any duties when it crosses Canadian customs. You just saved $50 in taxes.
