What is better for cooking? canola or olive oil. canola oil is more cost effective but if not as good as olive oil then i will totally switch to virgin olive oil?

This really isn't a health question. There are many cooking oils, maybe hundreds. From a health standpoint, limit use of highly saturated oils like lard, other animal fats, and coconut oil. Beyond that, personal preferences in taste vary widely. It also depends on how the oil is used, especially for frying. For example, olive oil may be a poor choice for frying. Google "cooking oil smoke point".

When it comes to olive oil , like wine there are different grades. Extra virgin is considered the best tasting and healthiest Regular olive oil has no health benefits

Olive oil is best not used for cooking as it has a low flash point and can catch fire. It is best used at room temperature and does have far better health benefits than canola oil. For cooking, perhaps avocado oil, peanut oil, or coconut oil are preferred by me, in that order.