Always check that the infant formula you are using is listed under the list of regulated infant formulas by Health Canada in order to keep your baby safe and healthy.
Infant formula is available in three formats: 1) ready-to-serve, 2) liquid concentrate that must be diluted with water, or 3) powdered that is to be mixed with water.  The powdered format is not sterile and presents a higher food safety risk hence it is recommended that higher risk babies should use ready-to-feed or liquid concentrate formats if possible.  Powdered formula can still be safely used in the higher risk babies when the sterile options are unavailable or unaffordable - powdered formula is often the cheapest option.  Powdered and all formats are suitable for all healthy, full term babies (born after 37 weeks) when prepared properly.
These higher risk babies include those:
Premature babies (born before 37 weeks of pregnancy) who are less than 2 months old based on their corrected age
Babies less than 2 months of age, who weighed less than 2500 grams at birth
Babies who have a weakened immune system, meaning they are more likely to get sick if exposed to germs