there's a difference between having harmless traditions that actually make a population happy or let them remember the suffering that they, as a nation, have gone through some time in the past because it's important not to forget, etc. HOWEVER, the monarchy is different because not only do they get a substantial amount of money from the state through taxes (and perhaps from other nations under the commonwealth, too) but they get a whole lot of needless attention from the media. as kowaru said, they're pretty much state-funded celebrities:
Last year the monarchy spent $64 million of public money (2.3% less than the previous year, adjusted for inflation) to fund its activities on behalf of the state, such as royal visits, the upkeep of palaces and official entertainment
Tell me that isn't a huge waste of taxpayer's money. Basically what you're advocating is that since we're already funding them with money they should stay around forever and remain filthy rich. I think her personal art collection is worth around 10 billion pounds. Not only is it a huge waste of money but why would you
want to be remembered as one of Britain's colonies and not an independent, functioning nation that could do without it? Look at India and Hong Kong, they too were under British control (the difference here being that they were not founded as nations under their rule) but they gained independence and don't look like nations who still have to suck on a teat to get by. but i digress, canada may have been founded by the brits but there's absolutely no reason in this day and age to remain under their "symbolic control"