I would like to integration payment gate into my site

Dear everyone,
I had a custom application site ( wrote buy CodeIgniter framework ) that was base on canada and they had federatedcanada payment gate.
I would like to integration some good provider payment gate that accept major card in UK to my site ( but i am really which one i need you guys advice as well )

one more thing the site had all city of canada i would like to change it as well

if you guys interested my job please tell which provider payment gate you will advice and how much and how long it will be done
Thanks