Standard visitor visa is a short term non-immigrant visa, maximum duration of stay is 6 months. Indian citizens can visit Ireland with a valid UK visa however entry port needs to be in UK.
Canada visitor visa is a non-immigrant visa issued for short term stay in Canada. On visitor visa you are allowed to stay for six-months from the day of entry.
As per CIC there are 2 types of visitor visas issued : Single and Multiple entry, however there is no option to select these options in form and I am not sure in which case single entry visas are issued.