How do I ack-grep exclude file type *.sql files or file size larger than >3MB?

According to the ack doc and man page you can ignore files with a particular extension by using --ignore-file=filter where filter is filtertype:filterargs. One of the filtertypes is ext for file extension. So try

--ignore-file=ext:sql

or since sql is one of the built-in types, you can just use

--nosql

I don't know about ack-grep but you can use find to exclude files larger than 3MB.

find . -size -3M -exec grep "foo" {} \;