So first off as a disclaimer, I am an undergraduate history student hoping to begin graduate studies in the next year. Most of my interest lies in Canada and the First World War, and have read an ungodly amount on the subject, so I think I am qualified to recount some of what I have learned.

You are absolutely correct that Canada had no choice in the matter to fight in World War One. As a Dominion of the British Empire, Canada's foreign affairs in 1914 was within British control and thus Canada had no power to declare war on its own. This power wouldn't rest in Canada proper until the 1931 Statute of Westminster was passed. That's not to say Canada was reluctant to join the war, even if they had no choice. There was an outpour of patriotic enthusiasm when the war began.

First, your assumption that all of Canada 'rallied hard' for the war effort is partly correct. Parts of Anglo-Canada rallied hard for the war the war initially. French Canada did not share the same sentiment. According to historian Desmond Morton, Ontario and the Western Provinces made up 73% of all enlistments, while consisting of 61% of Canada's population at the time. This was far more proportional than Quebec, which consisted of about 27% of the population however made up just 14% Canadian enlistments. This is not to say that Quebec as a province was simply slacking off in its support of the war though. Most of that figure above were Anglophone residents of Quebec, so clearly it was more of a French-English discrepancy rather than the province itself.

The discrepancy here is more related to the francophone-anglophone power struggle that is still present in Canadian politics. For example some at the time argued that the Minister of Militia, Sam Hughes, favored protestants over the predominantly Catholic French Canadians when establishing the CEF, with few of that demographic having being made officers. Without a doubt most would have wanted to serve in a French speaking battalion, with that being their first language and in some cases only language, but only 13 Francophone battalions were raised out of the 260 raised for the Canadian Expeditionary Force in total. The reluctance for French Canadians, and Canadians in general to serve overseas was further demonstrated by riots following the implementation of Canadian conscription under the Military Service Act. Many flat out refused to serve, and the police in Quebec did not enforce it either. These feelings culminated in riots that left 5 people dead in April of 1918. This reluctance to be conscripted was not unique to Quebec though. In total of the roughly 400,000 men deemed to be in 'Class 1' (Single men between 20-34) under the system, 380,000 applied for an exemption from service. Hopefully this illustrates that not all Canadians rallied hard for the war.

Yet you are right that there was great enthusiasm for the war in some parts of Canada. Desmond Morton writes that at the same time recruitment in Britain had slowed, Canadians were still enlisting in the CEF at record rates. Between fall 1915 and spring of 1916, the CEF had recruited 186,000 men. Given Canada's small population, that's no small feat. You're also right that there was an impressive response from farmers and the western provinces, as the Prairies have been acknowledged by historians to be the best recruiting ground for the CEF. I will list out some reasons Desmond Morton has acknowledged for why Canadians signed themselves up for this European war.

Economics is one reason. 1914 was a bad year economically for Canada, and the CEF offered a relatively good income. The prairies were in a bad spot in particular, as there had been a harsh winter and subsequent crop failure in that region which meant trouble for it's agricultural workers. The Maritimes and Ontario did not share the same fate. Joining the CEF not only paid a Private $1.10 per day, but their families could receive a separation allowance from the government, half of that pay assigned to them, and support from the Canadian Patriotic Fund (A charitable scheme meant to support families of soldiers overseas). This economic incentive to serve was reiterated by people all over the country. One logger mentioned in Morton's Book discussed how at best he could expect $22 dollars a month before he had enlisted in the 21st Battalion. A historian for the French-speaking 22nd Battalion found that most veterans reported that they too had enlisted because they couldn't find employment.

There was also an cultural aspect in Canada that can explain this too, in particular in Canadian masculinity. Patriotism was closely related to masculinity, and some that joining up and this outpouring of patriotism was a way to prove their manliness. This generation in Canada was brought up to believe that they were a part and the defenders of the British empire, and thus when Britain went to war many felt it was their duty to do so as well. Social pressures to conform to this idea existed too. In Saskatchewan, close to your example of Manitoba, a group of socialites signed an agreement to socially boycott those who did not enlist, writing that women 'foully wronged their manhood' by entertaining them while war raged in Europe. Likewise the infamous 'white-feather' campaign existed in Canada too as a way to pressure men to join up, and was referenced by some veterans to have been a reason they enlisted so they could avoid such shame and stigma.

So therefore your example of a 'rural farmhand in Manitoba', like all Canadians had varying reasons for enlisting. He could have underwent a period of unemployment due to the crop failures plaguing his province in the summer of 1914 when the war began, and saw the war and the CEF as a means for steady employment and pay for him and his family. On the other hand, he very well could have subscribed to the view that the war was an opportunity to prove his manliness, or that he was a part of the British Empire and ought to defend it, or he could have joined in response to some of the pressures different elements of society put on men when they didn't join up to serve overseas.

Unfortunately, I'm away from home right now and would have liked to pull out a Toronto newspaper my great-grandfather kept from 1914 after war was declared. The primary source would have better illustrated some of the attitudes in Canada, but alas I can't pull upon it in this response. I was unable to find any information as to the last part of your question as to whether there were fears of hostilities spilling over into Canada.

All the examples and statistics I used is from historian Desmond Morton's book 'When Your Number's Up'.

I would highly recommend Desmond Morton's works 'When Your Number's Up' and 'Fight or Pay', both regarding Canada and the First World War. The latter focuses more on Canadian society at home, and examines benefits available to families of servicemen at the time. Tim Cook has several books about Canada and the 1st World War, however most of them are on the actions and battles overseas rather than Canada at home.

Works Cited

Queens Own Rifles Museum and Archive, "CEF Rates of Pay,". https://qormuseum.org/history/timeline-1900-1924/the-first-world-war/cef-rates-of-pay/

Morton, Desmond. When Your Number's Up: The Canadian Soldier of The First World War (Toronto: Random House of Canada, 1993).