In Canada, federally, third party advertising on political issues during elections is allowed, but regulated with reporting requirements and spending limits.
Also corporate and union donations to political parties are banned and individual donation are limited to about $1,200 dollars per year.
Like the US we have constitutionally protected freedom of expression, but there is also section one which says, "The Canadian Charter of Rights and Freedoms guarantees the rights and freedoms set out in it subject only to such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society."
So freedom of expression can be limited in the name of democracy.