I'm a little confused, because the post says "1/2 month trip", which I read as "half-month trip", but since you say "until October", that suggests you mean "1 to 2 months".
The previous poster is right about a half-month trip: that's not nearly enough time to see the whole country. Two months would give you enough time to see a lot of Canada, but if you're thinking buses and trains rather than driving it gets more complicated (be warned that bus and train prices are fairly high here - look at the Greyhound.ca and ViaRail websites and input some possible desinations you're interested in to get a sense of things).
You could spend about 2 weeks exploring the main Toronto-Québec urban corridor. You can see Niagara Falls on a day trip to via bus, and the falls (along with the Maid of the Mist boat ride) are worthwhile even though the city of Niagara Falls is terribly touristy. After that, take trains to Ottawa, Québec, and Montréal, and spend 3-5 days in each of them, depending on what you want to see. Ottawa has Parliament, a lot of museums (Canadian History Museum, Canadian War Museum, and National Gallery are all very worth seeing), and excellent cycling paths along the canal and the rivers. Montréal has a nice old town (Vieux-Montréal); an excellent museum called Pointe-à-Calliére that lets you see the foundations of the city from the 1600s and has a lot of great historic exhibits; the former Olympic Park, which has a small indoor zoo (the Biodome) and a good botanical garden; and an excellent reputuation for dining and nightlife. Québec City is the oldest town in the US or Canada and still has a city wall and a great historic centre. It's a lot of fun to look around, and has a couple good museums (Musée de Civilisation and Musée des Beaux-Arts) as well.
If you're not going to drive, then fly either to Winnipeg (if you really want to get a sense of the scale of the prairies) or to Calgary (if you want to prioritize spending time in the mountains and on the Pacific Coast). I haven't taken buses or trains around the prairies, but there's only one train route and it doesn't allow for a lot of flexibility, so you might be better off with buses if you decide to go through the prairies. Regina is one of the nicer prairier cities and has an excellent park in the middle of town, as well as a good provincial museum. Moose Jaw is also an interesting place - the Tunnels of Moose Jaw tours take you through historic tunnels that were used a variety of ways through the city's history, including as living and working space for immigrant labourers and as a hiding place for rum-runners during Prohibition in the 1920s, when booze was smuggled from Canada to the US. I've taken both tours, and they're good, although the Prohibition-era one is pretty cheesy.
After you get to Calgary and have had a look around the city, take a bus to Banff or Lake Louise, and spend time hiking. There are bus tours that will take you from Banff to Jasper, although they're expensive. When you're done in the mountains, take either a bus (I think Greyhound is your only option) or a train (Via Rail runs from Jasper, but can be very late - when I took the train it was about three hours late leaving Jasper; on the upside, it's more comfortable than the bus and the section through the mountains passes some good scenery) to Vancouver. Spend a couple days Vancouver (highlights: Stanley Park hiking, Stanley Park seawall, Vancouver Aquarium, First Nations art galleries along Water St in Gastown, Granville Island, UBC Museum of Anthropology), then take the ferry from Horseshoe Bay to Nanaimo, and a bus from Nanaimo to Tofino or Uclulet to spend some time on the Pacific coast. There are buses from both Tofino and Uclulet to Long Beach, which is a very impressive beach (popular with surfers); there's also the gorgeous Wild Coast Trail in Uclulet along rocky coastline, and whale-watching and hot springs trips out of Tofino. When you're done, take the TofinoBus back to Victoria, spend a couple days in Victoria, and then fly back to Toronto from there. Bear in mind, however, that the transit for this leg of the trip will get very expensive (e.g.: it's an over-$100 bus ride just to go from Jasper to Banff, and about another $150 to take ViaRail from Jasper to Vancouver; buses to, from, and around the Tofino/Long Beach area are also pricey).
That covers a large section of Canada and is manageable in 2 months. The Atlantic provinces are completely out if you want to use buses and trains - I've checked before, and it's virtually impossible to get around the them without a car.
It is more convenient to get around by car, though, and it allows you to see a lot of places that you can't reach by bus or train, but it's not impossible to get around and see the major sights without a car. And a lot of the posts on this site are people complaining about how expensive it is to rent a car and drive it one-way across the country. If you're capable of and legally allowed to drive in Canada, I'd spend some time comparing prices of different transportation options before you make a decision.
