If the government decided to have a much higher proportion of long-term bonds than it currently does, the impact on public finances would be an increase in interest rates, since there may be no demand for them. It is also possible that demand may be strong. The people at the Bank of Canada and the Department of Finance would be in a good position to provide you with information on that.
Generally, people at the Bank of Canada and the Department of Finance see the numbers the same way we do. With such low interest rates, if there was a demand for more long-term bonds, the government would probably move in that direction. However, if the government decided to go beyond what the market can absorb, the interest rates would be higher for those 30-year bonds, to use that example, but probably also for other long-term bonds of less than 30 years.
In short, the interest rates would be higher, so the government would have to pay more for the financing.