This doesn't make it very easy for us to compare vowels between languages or dialects. How do we write the difference between monophthongal [o] in Winnipeg English and a monophthongal [o] in Scottish English or a monophtongal [o] in Italian?
The IPA symbols for vowels are better seen as similar to international standards for things like colour names. "Red" paint has to be of a certain hue and intensity, otherwise modifiers have to be added: "dull brick red". Similarly, the symbol [o] refers to a vowel made with the tongue body in a relatively exact place (and which will therefore have the formants at certain frequencies). A very narrow transcription would record any deviation from this place.
So the symbol  does not stand for the vowel in English father. It stands for the vowel that is the furthest back and the lowest possible vowel in the vowel space (the vowel with the highest F1 and the closest F2 to F1). Period. Canadian English just happens to have the vowel in father very close to this position. When we make statements about other dialects, for example, when we say that the typical pronunciation of the vowel of father in the northern U.S. is more front than , we aren't saying that the Canadian pronunciation is more deserving of the symbol  because it is somehow better, we are merely saying that the northern U.S. pronunciation is not in the lowest, backest part of the vowel space.
The idea of cardinal vowels originated with Daniel Jones.
The cardinal vowel chart organizes the vowel space between the two most extreme tongue body positions: high front [i] and low back .
The high/low dimension is divided into four equally spaced levels. These correspond to the vowels we have been describing as:
The equal spacing between the height levels can be determined articulatorily (make your tongue body move in four equal steps from high to low) or acoustically (divide the F1 dimension into four levels from lowest to highest). Jones' original proposal only considered the articulatory definition.
Other vowels are placed on the vowel chart using these cardinal vowels as landmarks.
The eight vowels seen so far are called the primary cardinal vowels. The secondary cardinal vowels are obtained by using the opposite lip-rounding on each primary cardinal vowel. The primary and secondary cardinal vowels are often referred to by a number as well as by their symbols.
On the IPA vowel chart, the rounded vowels are always listed to the right
of the corresponding unrounded vowel. (Besides being consistent, this
also reflects their relative positions on formant graphs. Recall that lip
rounding will lower F2, and lower F2s are toward the right end of the standard