Lets make some assumptions.
1. No other income aside from your pension (overly simplistic) - you'll need $26.1k per year to make your desired $45k/year.
2. You live to 85 yrs, you'll need $652k from other sources to be withdrawn. To get to the amount - subtract your current savings (say $200k for this example) and you'll need to grow your investments by $452k.
If you've got 20 years to do that, say you can save $10000/yr = $200k, with $242k required to come from portfolio growth. To achieve this, you'll need around 3.5-4% real return growth (inflation adjusted).
Based on that desired rate of return (3.5-4%) you can use this to determine your 'ideal' asset allocation. For example, based on many rolling 20yr periods, the S&P 500 can return about 11% (before inflation), so you know you WON'T need 100% in equities.
Basically, you'll want to set expected rates of returns for each asset class, then make model portfolios with different % of each class and see if you can produce the required return. Bonds typically yield close to or less than inflation, equities roughly 11%, real estate about 2-3% above inflation etc.
Note this is a rough and dirty example, keep reading, figure out how much you think you'll need, get your assumptions of growth rates and inflation as accurate as possible, then you should be able to get at how much risk you'll need to take.
My view of asset allocation is that there are multiple tiers - in order of importance (my opinion

)
1. Asset type (cash, bonds/fixed income, equities, real estate).
2. Subtypes (within bonds: government vs. corporate, equities: Large, mid, small capitalization, real estate: residential, retail, corporate).
3. Country (although economies all seem very closely correlated these days)
4. Sectors (bonds: muni's vs. federal/provincials, grades of the coupons, equities: 10 sectors (tech, energy, financials etc.).
5. Individual assets/holdings within each sector.