For proof of funds you need to show liquid funds so fixed deposits will create a problem because you need to show that you have cash available to be able to support your travels. Have you or your spouse ever attempted to immigrate or study/or work abroad. Do you have family in Canada and do your close family members (siblings and parents) still live in Sri Lanka? Are you employed or have you been employed in the past few years? 4 months is very long visit for a married adult unless for a specific reason. Traveling for a friend’s 50th birthday party is not a very good reason to travel especially not for family. Are they having a large party at an event space? It should be a more elaborate celebration similar to a wedding to justify travel to Canada. There will be likely be concerns that you are trying to find a way to remain in Canada for a longer period of time and perhaps try to find employment.