is there any rights to being able to visit my nieces

Nope. They are not your kids. You have no rights whatsoever regarding them.

 

There may be exceptions in BC.

BC's Family Law Act: Orders respecting contact

59 (1)On application, a court may make an order respecting contact with a child, including describing the terms and form of contact.

(2)A court may grant contact to any person who is not a guardian, including, without limiting the meaning of "person" in any other provision of this Act or a regulation made under it, to a parent or grandparent.

(3)The court may make an order to require the parties to transfer the child under the supervision of, or require contact with the child to be supervised by, another person named in the order if the court is satisfied that supervision is in the best interests of the child.

SBC 2011, c 25 | Family Law Act | CanLII

Though the law mentions grandparent, it expressly does not limit the definition of "person" to just grandparent, and it does mention "the best interests of the child."

In Simmons vs Simmons the court awarded visitation to paternal grandparents over the objection of the mother.

2016 NSCA 86 (CanLII) | Simmons v Simmons | CanLII

While an exception might not apply as strongly to aunts and uncles as it does to grandparents, it does seem to be available, depending on what the court deems to be "the best interests of the child."

 

To be clear though, the laws and cases that adjusterjack listed will require would require you to go to court and get an order from said court to see the kids. There is no law that simply gives you the right to see the kids.

 

Why are the parents mad at you?

 

Yes your sister can stop you from seeing her children. 100%. You have no legal standing to demand to see her children.

 

You know that for sure under Canadian law, Leslie?

 

I honestly don't care. I didn't see other posts before I posted my response yesterday. And I don't really care now. So...yeah.

 

My point is that unless you know the law of another country, you cannot make such declarative statements about non-US law. Whether you saw the other responses or not.