I know the IELTS exam dates are usually in the future sometime, so if you don't want to delay your application timeline - you may submit your application package without the IELTS. However, like Kenny04 suggests, please include a letter informing CIC that you are planning on taking the IELTS (give proof of date/time/etc) with the initial application. Make sure you send the results to CIC as soon as you get them or you risk getting low scores under the language profeciency sections of the assessment.
Keep in mind that unless you've lived in an English/French speaking country for several years or graduted from universities in those countries, a proficiency letter is usually not a good idea. Nothing beats a conclusive IELTS score.
Good luck.